Mutliple lamination high density interconnect process and structure employing thermoplastic adhesives having sequentially decreasing TG 's

Abstract

A high density interconnect structure incorporating a plurality of laminated dieletric layers is fabricated using thermoplastic adhesive layers of progressively lower glass transition temperature in order to maintain the stability of the already fabricated structure during the addition of the later laminations. This structure also facilitates the removal of only a portion of the high density interconnect structure where a fault in the system can be corrected in one of the upper layers of the high density interconnect structure.

What is claimed is: 
     
       1. A high density interconnect structure comprising: a plurality of semiconductor chips each having contact pads on a first surface thereof;   a first layer of dielectric material bonded to said semiconductor chips, said first layer of dielectric material comprising first lower and first upper sublayers, said first lower sublayer being thermoplastic and having a first glass transition temperature T g1 , said first upper sublayer being stable over a range of temperatures above said first glass transition temperature, said first layer of dielectric material having via holes therein disposed in alignment with at least some of said contact pads;   a patterned first metallization layer disposed on said first layer of dielectric material and extending into contact with at least some of said contact pads in said via holes in said first layer of dielectric material;   a second layer of dielectric material bonded to said first metallization layer and exposed portions of said first layer of dielectric material, said second layer of dielectric material comprising second lower and second upper sublayers, said second lower sublayer being thermoplastic and having a second glass transition temperature T g2 , said second upper sublayer being stable over a range of temperatures above said second glass transition temperature; and   said first glass transition temperature being higher than said second glass transition temperature.   
     
     
       2. The high density interconnect structure recited in claim 1 wherein: said second layer of dielectric material has via holes therein disposed in alignment with some of said contact pads and/or portions of said first metallization layer; and   said high density interconnect structure further comprises: a patterned second metallization layer disposed on said second layer of dielectric material and extending into contact with selected contact pads and/or selected portions of said first metallization layer in said via holes in said second layer of dielectric material.     
     
     
       3. The high density interconnect structure recited in claim 2 further comprising: a third layer of dielectric material bonded to said second metallization layer and exposed portions of said second layer of dielectric material, said third layer of dielectric material comprising third lower and third upper sublayers, said third lower sublayer being thermoplastic and having a third glass transition temperature T g3 , said third upper sublayer being stable over a range of temperatures above said third glass transition temperature, T g3  being less than T g2 .   
     
     
       4. The high density interconnect structure recited in claim 3 wherein: said third layer of dielectric material has via holes therein disposed in alignment with some of said contact pads and/or portions of said first metallization layer and/or portions of said second metallization layer; and   said high density interconnect structure further comprises: a patterned third metallization layer disposed on said third layer of dielectric material and extending into contact with selected contact pads and/or selected portions of said first metallization layer and/or portions of said second metallization layer in said via holes in said third layer of dielectric material.     
     
     
       5. The high density interconnect structure recited in claim 1 wherein: said second layer of dielectric material has via holes therein disposed in alignment with at least some portions of said first metallization layer; and said high density interconnect structure further comprises: a patterned second metallization layer disposed on said second layer of dielectric material and extending into contact with at least some portions of said first metallization layer in said via holes in said second layer of dielectric material.     
     
     
       6. The high density interconnect structure recited in claim 1 wherein: said first and second upper sublayers are thermoset polymers.   
     
     
       7. The high density interconnect structure recited in claim 6 wherein: said first and second upper sublayers are thermoset polyimide.   
     
     
       8. The high density interconnect structure recited in claim 6 wherein: said first lower sublayer comprises polyetherimide; and said second lower sublayer comprises a siloxanepolyimide.   
     
     
       9. The high density interconnect structure recited in claim 6 wherein: said first lower sublayer comprises a sulfonylpolyetherimide; and   said second lower sublayer comprises polyetherimide.   
     
     
       10. The high density interconnect structure recited in claim 6 wherein: said first lower sublayer comprises a sulfonylpolyetherimide; and   said second lower sublayer comprises a siloxanepolyimide.   
     
     
       11. The high density interconnect structure recited in claim 6 wherein: said first lower sublayer comprises a polyetherimide; and   said second lower sublayer comprises a polyester.   
     
     
       12. The high density interconnect structure recited in claim 1 wherein: at least one of said upper sublayers is thermoplastic.   
     
     
       13. The high density interconnect structure recited in claim 12 wherein: said first and second upper sublayers are thermoplastic.   
     
     
       14. In a method of fabricating a high density interconnected system of the type including a plurality of electronic chips, a high density interconnect structure including a layer of dielectric material bonded to said chips and a pattern of conductors disposed on or in said dielectric material, the conductors of said high density interconnect structure electrically interconnecting said electronic chips, the improvement comprising: a) laminating a first dielectric layer to said chips using a first thermoplastic adhesive having a first glass transition temperature T g1  ;   b) forming via holes in said first dielectric layer and said first adhesive in alignment with at least some contact pads of said chips;   c) forming a patterned first metallization layer on said first dielectric layer, said first metallization layer including conductors which extend into ohmic contact with contact pads in said via holes;   d) laminating a second dielectric layer to said first metallization layer and exposed portions of said first dielectric layer using a second thermoplastic adhesive having a second glass transition temperature T g2  which is lower than said first glass transition temperature, this laminating step being performed at a low enough temperature that said first dielectric layer remains fixed, whereby said first metallization layer and its contacts to said contact pads are not adversely affected by this laminating step.   
     
     
       15. The improvement recited in claim 14 further comprising the steps of: e) forming second layer via holes in said second dielectric layer and said second adhesive in alignment with said contact pads and/or said first metallization layer; and   f) forming a patterned second metallization layer on said second dielectric layer, said second metallization layer including conductors which extend into ohmic contact with conductors of said first metallization layer and/or said contact pads in said second layer via holes.   
     
     
       16. The improvement recited in claim 15 further comprising the step of: f) laminating a third dielectric layer to said second metallization layer and exposed portions of said second dielectric layer using a third thermoplastic adhesive having a third glass transition temperature T g3  which is lower than said second glass transition temperature, this laminating step being performed at a low enough temperature that said first and second dielectric layers remain fixed, whereby said second metallization layer and its contacts to said contact pads and/or said first metallization layer are not adversely affected by this laminating step and said first metallization layer and its contacts to said contact pads are not adversely affected by this laminating step.